1. Field of the Invention
The invention relates to storage systems.
2. Related Art
Computer storage systems are used to record and retrieve data. One way storage systems are characterized is by the amount of storage capacity they have. The capacity for storage systems has increased greatly over time. One problem in the known art is the difficulty of planning ahead for desired increases in storage capacity. A related problem in the known art is the difficulty in providing scalable storage at a relatively efficient cost. This has subjected customers to a dilemma; one can either purchase a file system with a single large file server, or purchase a file system with a number of smaller file servers.
The single-server option has several drawbacks. (1) The customer must buy a larger file system than currently desired, so as to have room available for future expansion. (2) The entire file system can become unavailable if the file server fails for any reason. (3) The file system, although initially larger, is not easily scalable if the customer comes to desire a system that is larger than originally planned capacity.
The multi-server option also has several drawbacks. In systems in which the individual components of the multi-server device are tightly coordinated, (1) the same scalability problem occurs for the coordinating capacity for the individual components. That is, the customer must buy more coordinating capacity than currently desired, so as to have room available for future expansion. (2) The individual components are themselves often obsolete by the time the planned-for greater capacity is actually needed. (3) Tightly coordinated systems are often very expensive relative to the amount of scalability desired.
In systems in which the individual components of the multi-server device are only loosely coordinated, it is difficult to cause the individual components to behave in a coordinated manner so as to emulate a single file server. Although failure of a single file server does not cause the entire file system to become unavailable, it does cause any files stored on that particular file server to become unavailable. If those files were critical to operation of the system, or some subsystem thereof, the applicable system or subsystem will be unavailable as a result. Administrative difficulties generally increase to due to a larger number of smaller file servers.
Accordingly, it would be advantageous to provide a method and system for performing a file server system that is scalable, that is, which can be increased in capacity without major system alterations, and which is relatively cost efficient with regard to that scalability. This advantage is achieved in an embodiment of the invention in which a plurality of file server nodes (each a pair of file servers) are interconnected. Each file server node has a pair of controllers for simultaneously controlling a set of storage elements such as disk drives. File server commands are routed among file server nodes to the file server node having control of applicable storage elements, and in which each pair of file servers is reliable due to redundancy.
It would also be advantageous to provide a storage system that is resistant to failures of individual system elements, and that can continue to operate after any single point of failure. This advantage is achieved in an embodiment of the invention like that described in co-pending application Ser. No. 09/037,652 filed Mar. 10, 1998, in the name of the same inventor, titled Available File Servers”, U.S. Pat. No. 6,317,844, hereby incorporated by reference as if fully set forth herein.